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Section 26 USB 2.0 Host/Function Module
Page 1542 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
The timing at which the operation of the buffer flush function varies depending on the value set
for the IITV bit.
If IITV = 0
The buffer flush operation starts from the next frame after the pipe becomes valid.
In any cases other than IITV = 0
The buffer flush operation is carried out subsequent to the first normal transaction.
Figure 26.21 shows an example of the buffer flush function of this module. When an unanticipated
token is received prior to the interval frame, this module sends the written data or a zero-length
packet according to the buffer state.
SOF
Transfer enabled
Buffer A
Buffer B
Empty Writing Writing ended Transfer enabled
Buffer flush operation is carried out
Empty Writing Writing ended
Empty Writing Writing ended
Figure 26.21 Example of Buffer Flush Function Operation
Figure 26.22 shows an example of this module generating an interval error. There are five types of
interval errors, as shown below. The interval error is generated at the timing indicated by (1) in the
figure, and the IN buffer flush function is activated.
If an interval error occurs during an IN transfers, the buffer flush function is activated; and if it
occurs during an OUT transfer, an NRDY interrupt is generated.
The OVRN bit should be used to distinguish between NRDY interrupts such as received packet
errors and overrun errors.
In response to tokens that are shaded in the figure, responses occur based on the buffer memory
status.
1. IN direction:
If the buffer is in the transmission enabled state, the data is transferred as a normal
response.
If the buffer is in the transmission disabled state, a zero-length packet is sent and an
underrun error occurs.
2. OUT direction:
If the buffer is in the reception enabled state, the data is received as a normal response.
If the buffer is in the reception disabled state, the data is discarded and an overrun error
occurs.